1. Field of the Invention
The invention relates to a steering and manoeuvering system for water-born vessels with two individually turnable propulsion units arranged at the stern portion of the vessel and mutually spaced athwartships. These units may be such as jet units, turnable so-called thrusters or turnable propeller units of the "AQUAMATIC", "Z-DRIVE" type or the like, (but not propeller units with a stationary propeller shaft and a separate rudder).
2. Prior Art
A first type of known steering and manoeuvering system for vessels with such double propulsion units includes an actuating turning device, which is actuable by a steering control, e.g. a lever or a wheel, and keeps the propulsion units parallel while being turned, and an actuating drive device, which is actuable by a power control for adjusting the propulsive power ahead or astern of the respective propulsion unit. The vessel can thus be steered for sailing ahead or astern in a desired starboard/port direction, as well as for executing a rotating or turning movement (one unit set for propulsion ahead and the other one for propulsion astern) which can be to advantage in manoeuvering in ports, harbours and other cramped situations. It is not possible to achieve pure athwartships movement with such a system, however. Athwartships movement namely requires that both propulsion units can be turned in opposite angular directions with opposing directions of propulsion.
In a second type of known steering and manoeuvering system (U.S. Pat. No. 3,976,023) all steering functions are achieved by a single controlling joystick which is movable in two dimensions. When the joystick is moved forwards/backwards the combined propulsion effect is increased ahead or astern (by different adjustments of the turning angle) and when the joystick is moved sideways port/starboard steering action is achieved to port or starboard. The power of the propulsion units can be regulated at the same time by pulling out or depressing a knob on the joystick. Turning and athwartships movement of the vessel can be achieved for certain positions of the joystick.
Such a steering and manoeuvering system can indeed appear to be simple, since only one lever is used, but even so it requires that the steersman of the vessel with this system is given extensive training in order to master different manoeuvres, particularly manoeuvers in harbours and ports. In addition, with this system it is difficult to compensate for external forces, e.g. those coming from wind and current, which act on the vessel in a translatory and/or rotary direction.